I made some sandals recently with 9 oz. shoulder as the sole. For casual use, that’s fine, esp if one glues a piece of rubber to the bottom. Don’t bother with a shank or stacking more layers than necessary. All that will do is make it hard, inflexible, and uncomfortable. Shanks are there for shoes with a separate heel where the sole drops to the toe, like in a dress shoe or cowboy boot. I guess some high-heeled “sandals” may have a shank, but it wouldn’t be straight like a popsicle stick anyway.
Get that basic pattern, and then the world is your oyster as far as design goes. A good pattern to start with, if you don’t have one already, is the Dieselpunk.ro pattern.